In general, the high-frequency rectangular wire is used for coils and the like of the AC motor and the high-frequency electrical equipment. This is also applied to motors for a high-speed railroad vehicle, in addition to motors for a hybrid vehicle (HV) and an electric vehicle (EV). Conventional rectangular wires are composed by stacking rectangular metallic bodies each having a rectangular shape of a cross-section and an insulative enamel film or oxide film formed on the outer periphery of the rectangular metallic body (for example, see Patent Literature 1 or 2).